There has been a continuous effort to decrease the neurotoxicity of iodinated radiographic contrast materials ever since their use as a diagnostic tool. These contrast materials are neurotoxic when applied directly to the central nervous system, but this toxicity is usually minimized by the blood-brain barrier (BBB) which keeps contrast materials within the vascular compartment and separate from the nervous tissue. However, the contrast materials frequently injure the BBB resulting in transient and sometimes permanent clinical neurological deficits. Of the several mechanisms proposed for the BBB injury with resultant permeability of the vascular contents into the nervous tissue, it has been suggested that there is a direct morphological alteration (irreversible and/or reversible) of the BBB following cerebral angiography. It is also suggested that these alterations are due to the hyperosmolar and/or chemical properties of the contrast materials. This investigation proposes to use light and electron microscopy to delineate the morphological alterations or difference of BBB permeability between the various contrast materials currently used for cerebral angiography. In addition, assessment of both the hyperosmotic and chemical properties of the angiographic contrast materials, as related to BBB changes, will be implemented by correlating physiological and morphological parameters. Assessment of the BBB at both the vascular and choroid plexus levels will be done following a clinically simulated cerebral angiography. The principal investigator is very familiar with light and electron microscopic techniques and their correlation with physiological and clinical data. Light and electron microscopy has rarely been used to evaluate this proposed investigation. Assessment of this investigation utilizing both morphological and physiological parameters has also been rarely implemented in previous studies.